The present invention relates generally to electronic connector systems and, more specifically, to low-profile connector systems for pluggable electronic modules, such as transceiver modules for high speed fiber optical communications.
Historically, electrical and opto-electric modules have been connected to printed circuit boards with solder pins. Conventional approaches for soldering the pins to the circuit board include reflow soldering and hand soldering. Although solder reflow is an effective technique for electrically connecting a module to a circuit board, the heat required to achieve reflow tends to be detrimental to heat sensitive components within the module, such as plastic optical components which tend to warp or otherwise distort at high temperatures. Furthermore, to ensure that modules are capable of withstanding the environmental conditions associated with reflow soldering, the industry utilizes high temperature materials that add cost to the modules. Since most modules will be used in more moderate climates (e.g., an air-conditioned office building), the modules are therefore xe2x80x9cover-engineeredxe2x80x9d simply to ensure that they can withstand the reflow soldering process.
To avoid exposing the module to harsh conditions during reflow soldering, often electronic modules are hand soldered instead to a printed circuit board. The need for hand soldering, however, dramatically increases the cost of system comprising such modules.
Aside from the problems associated with soldering the module to the circuit board, there is the added inconvenience that, if a single module fails on a circuit board, which may support many such modules, the entire circuit board must be removed for service.
Therefore, there is a need for a solderless connection of a module to a circuit board. To this end, several pluggable module designs and standards have been introduced in which a pluggable module plugs into a receptacle which is electronically connected to a host circuit board. For example, a well-known type of transceiver developed by an industry consortium is known as a gigabit interface converter (GBIC) or serial optical converter (SOC) and provides an interface between a computer and a data communication network such as Ethernet or Fibre Channel. These standards offer a generally robust design which has been well received in industry.
Although these conventional pluggable designs have been used successfully in the past, they tend to be unsuitable for miniaturization which is an ever-constant objective in the industry. It is desirable to miniaturize transceivers in order to increase the port density associated with the network connection, such as, for example, switch boxes, cabling patch panels, wiring closets, and computer I/O. Recently, a new standard has been promulgated and is referred to herein as the small form factor (SFF) standard which specifies an enclosure height of 9.8 mm and a width of 13.5 mm and a minimum of 20 electrical input/output connections. In addition to miniaturizing the module, it is also desirable to increase its operating frequency. For example, applications are quickly moving from the sub-gigabit realm to well over a gigabit. Conventional pluggable module configurations, however, cannot meet these parameters.
Miniaturizing a module while maintaining or even increasing its operating speed, presents a number of design problems particularly in applications in which data transmission rates are high, e.g., in the range of 1-10 Gbs (Gigabits/second). Of particular concern is reducing electromagnetic interference (EMI) emissions. Due to FCC regulations, there is a need not only to minimize the EMI emissions of the module, but also to contain the EMI emissions of the host system in which the module is mounted regardless of whether a module is plugged in to the receptacle. In conventional designs, this EMI shielding was achieved by using conductive spring-loaded door which was capable of swinging shut and closing the receptacle when the module was removed. Conventional receptacles also had spring clips to ground the receptacles to the opening or xe2x80x9cbezel openingxe2x80x9d of the host system through which the receptacle protrudes. Providing space for spring-loaded doors and spring clips on the receptacle tends to be problematic if not impossible in miniaturized configurations. Additionally, the small size presents problems in dissipating heat from the module and incorporating traditional mechanisms for ejecting and retaining the module and for electrically connecting the module to the host circuit board.
It has also been found that providing solutions for the aforementioned EMI and miniaturization problems is further complicated by the dimensional various in the industry with respect to bezel opening position vis-a-vis the host circuit board. While many applications require that the bottom of the bezel opening be flush with the top of the circuit board, some applications require that the bezel opening be raised from the top of the host circuit board. For example, the PCI Local Bus Specification, Revision 2.2 specifies that the bottom of the bezel opening must be 0.4xc2x10.1 min above the host circuit board. As used herein, the distance between the bottom of the bezel opening and the top of the host circuit board is refereed to as the xe2x80x9cbezel opening offset.xe2x80x9d To function properly, a suitable receptacle must be able to accommodate this bezel opening offset while also addressing the EMI and miniaturization concerns mentioned above.
Therefore, there is a need for a versatile module design that conforms to the various dimensional standards, while minimizing EMI emissions and providing convenient pluggable operation. The present invention fulfills this need among others.
The present invention provides for a pluggable module and receptacle system that facilitates miniaturization and high operating frequencies by effectively shielding EMI emissions to eliminate leaks and conduct EMI to ground, and by synergistically using components to eliminate conventional discrete mechanisms and their attendant bulk. The present invention also provides for a module and receptacle system which is versatile and able to accommodate a variety of dimensional requirements and bezel opening offsets without comprising the EMI shielding and without a substantial change in the components used.
EMI shielding is achieved by implementing one or more features that serve to minimize gaps through which EMI can escape, and/or to enhance grounding of the receptacle. One such feature is a receptacle housing in which all of its sides except the front comprise conductive walls for blocking EMI. This way, when the receptacle is mounted within a host system and is exposed to the host system""s internal EMI, all of the housing sides exposed to the EMI, including the back and the bottom, are conductive and thus suitable for conducting the EMI to ground. Preferably, the housing is electrically connected to ground through a number of elongated members. Another feature for minimizing gaps through which EMI can escape is the use of containment members. Containment members extend downward from the receptacle, preferably between elongated members, and essentially form a picket fence along with the elongated members to prevent EMI emissions.
In addition to minimizing gaps through which EMI can escape, the module and receptacle system of the present invention is extremely well suited for conducting EMI to ground. This grounding is achieved principally by grounding contacts on the front end of the module and grounding tabs around the front opening on the receptacle. This way, the grounding contacts provide a grounding path from the module to the receptacle and the grounding tabs, in turn, provide a grounding path from the receptacle to the host chassis. Preferably, the grounding tabs are cut from the receptacle housing walls and elongated such that the grounding tabs are longer than the respective section of the wall from which each grounding tab was derived. Such a configuration prevents the grounding tabs from being deflected into the receptacle cavity. This arrangement is particularly preferably in small form factor configurations in which there is no room in the receptacle cavity to accommodate anything other than the module. To enhance the grounding of the module to the receptacle while the module is being inserted therein, the receptacle housing defines rows of ventilation holes, which, in turn, define ground paths therebetween. By spacing the grounding contacts on the module to correspond to the spacing of the grounding paths on the receptacle, the grounding contacts will slide along the grounding paths during the module""s insertion and withdraw from the receptacle, thereby ensuring the module""s grounding. Further enhancements to grounding include a latch which serves not only to retain the module within the receptacle, but also to provide a grounding path from the front of the module to the front of the receptacle and to provide an extra picket in the EMI fence as mentioned above.
The receptacle of the present invention is also able to accommodate variations in bezel opening offset while maintaining adequate EMI shielding by tilting the front of the receptacle upward with respect to the host circuit board. It has been found that tilting the receptacle to accommodate bezel opening offset overs a number of advantages over other approaches such as raising the entire receptacle in a parallel orientation with respect to the host circuit board or changing the dimensions of the receptacle entirely.
First, by tilting the front of the receptacle upward, the rear end of the receptacle remains close to the host circuit board, thereby minimizing the gap between the bottom the receptacle and the host circuit board. Minimizing this gap is important in minimizing EMI emissions since the rear of the receptacle contains the receptacle connector which effects the electronic transmissions between the module and the host circuit board. These electrical transmission render the rear of the receptacle especially susceptible to EMI emissions, particularly at high operating frequencies. Further, since the receptacle must have an opening on its bottom side near its rear to accommodate the receptacle connector, the EMI shielding of the housing is compromised to some degree in this region. Therefore, it is particularly advantageous for the receptacle to be tilted down in the rear to minimize gaps where EMI emissions are particularly high and the receptacle has limited bottom shielding.
Aside from EMI shielding, another advantage of tilting the recepticle such that its rear end remains close to the host circuit board is minimizing the distance the receptacle connector needs to couple signals between the host circuit board and the module. Minimizing this coupling distance is important for operating at high frequencies since longer distances often equate to higher impedance and a general reduction in the electrical performance of the system.
Another advantage of tilting the cage to accommodate different bezel opening offset is the ability to minimize reconfiguring the receptacle and module components. In fact, it has been found that the receptacle may be tiled with just minor modifications to the lower portion of the receptacle. Thus, the receptacle connector and other components of the receptacle remain the same. It is well known that minimizing the number of components used by a system in various applications not only reduces the capital costs of initially tooling the components, but also reduces inventory costs. Furthermore, since many of the same components can be used among the tilted and non-tilted versions of the receptacle, the performance of the receptacle is basically the same among the various versions. For example, since the same receptacle connector can be used, similar impedance and electrical performance between the coupling of the module and the host circuit board can be expected. Consequently, modules perform equally in well in tilted and non-tilted applications. Such similar performance avoids the need to modify the module according to particular bezel opening offset applications. This is a significant advantage as it reduces costs and inventory needs, while increasing reliability and simplicity in the industry.
The module and receptacle system of the present invention also employs components of the receptacle synergistically to avoid separate mechanisms and components which add bulk and cost to the system. For example, rather than using a conventional connector to effect the module""s connection to the receptacle connector, a card edge connection configuration is used. Additionally, the ejection mechanism uses a resilient back portion of the receptacle to urge the module out once the latch is released. The more efficient use of components within the module and receptacle provide for the elimination of other components and thus a general reduction in the system""s bulk. This naturally facilitates miniaturization which, as mentioned above, is an ever-present objective in module design.
Accordingly, one aspect of the invention is a receptacle having a housing that shields EMI on all sides exposed to the EMI of the host system. In a preferred embodiment, the receptacle comprises: (a) a housing having a front, a back wall, a top wall, a bottom wall, and side walls and defining a cavity for receiving a module, the bottom wall having a bottom opening to receive a receptacle connector, the front having a front opening to receive the module, the walls comprising a conductive material; (b) a plurality of elongated members extending down from the housing past the bottom wall and adapted for electrical connection to a host circuit board such that the walls are electrically connected to the host circuit board; and (c) at least one standoff extending down from the housing, the standoff being more toward the front of the housing than the rear, when the housing is mounted to the host circuit board, the standoff contacts the circuit board and causes the front of the housing to be raised above the rear of the housing, the front of the housing being raised above the host circuit board by a distance approximately that of the bezel opening offset.
Another aspect of the invention is a pluggable module system having the receptacle as described above. In a preferred embodiment, the system comprises: (a) a receptacle mounted to a host circuit board within a chassis of a host system, the chassis having a bezel opening which has an offset a certain distance above the host circuit board, the receptacle comprising a housing having a front and rear, a back wall, a top wall, a bottom wall, and side walls and defining a cavity for receiving a module, the bottom wall having a bottom opening to receive a receptacle connector, the front having a front opening to receive the module, the walls comprising a conductive material and being electrically connected to the host circuit board, the housing also comprising at least one standoff extending down from the housing, the standoff being more toward the front of the housing than the rear, when the housing is mounted to the host circuit board, the standoff contacts the circuit board and causes the front of the housing to be raised above the rear of the housing, the front of the housing being raised above the host circuit board by a distance approximately that of the bezel opening offset; (b) a receptacle connector electrically connecting to the host circuit board and protruding into the cavity through the bottom opening, the receptacle connector being adapted for electrically connecting the module to the host circuit board; and (c) a module comprising a module housing having a front end and a back end and being adapted for insertion into the receptacle and grounding contacts configured for electrical connection to the housing of the receptacle.
Yet another aspect of the invention is a module which eliminates the use of a conventional connector and uses instead a card edge connection approach. In a preferred embodiment, the module comprises: (a) a housing having a front end and a back end and being adapted for insertion into a housing mounted to the host circuit board; (b) a module circuit board at least partially mounted within the housing such that at least an edge portion of the circuit board is not contained within the housing, the edge portion comprising pads on opposing sides of the module circuit board, the pads being suitable for forming an electrical connection with contacts in the mating connector.